The present invention relates generally to location detection in wireless networks and, more particularly, to location detection in wireless mesh networks installed in an industrial setting.
The combination of technology advances in wireless technology, low power microprocessors, integrated circuits, measurement and control techniques, and energy storage has enabled the development of low-cost, low power devices. Networking wireless devices together into a sensor network that is able to meet the reliability, latency, real-time, and performance requirements of process automation applications, while at the same time taking into consideration the practical limits on available resources is a challenging task. Wireless signal strength varies in time, and wireless nodes come and go. Data is routed dynamically on different paths, and batteries have a finite amount of energy. To meet these demands, network management techniques must be able to form the overall network topology using information reported by the devices and the network itself and then schedule and optimize the overall network for latency, power, and throughput.
Managing latency while at the same time conserving power is a problem facing wireless sensor networks today. To minimize latency, communications need to be organized so that packets are not delayed en-route from source to destination. In the industrial setting, low power nodes must operate for long periods of time, usually many years, often unattended. To minimize energy usage devices should be kept in a low-power mode as much as possible.
At the communication distances typical in sensor networks, listening for information on the radio channel consumes approximately the same amount of power as data transmission. Further, the energy consumption of an idle device is approximately the same as that of a device in receive mode. As a result, the most effective way to save power is to turn the radio and the device itself off during idle times. Turning the device off implies advance knowledge about when the device will be idle and when it should power back on. The approach taken in some industrial sensor network protocols, such as WirelessHART, is to configure the device with knowledge about when it should wake up, perform some function, and go back to sleep. This configuration is performed by a network manager and is called time scheduling.
One approach to address this is with the use of time synchronized wireless technologies such as Time Division Multiple Access (TDMA) utilized by WirelessHART. WirelessHART is a secure networking technology operating on the 2.4 GHz ISM radio band utilizing IEEE 802.15.4 compatible direct-sequence spread spectrum (DSSS) radios with channel hopping on a packet by packet basis.
Scheduling is performed by a centralized network manager which uses overall network routing information in combination with communication requirements that devices and applications have provided. The schedule is subdivided into slots and transferred from the network manager to individual devices. Devices are only provided with the slots for which they have transmit or receive requirements. The network manager continuously adapts the overall network graph and network schedule to changes in network topology and communication demand.
The network manager also initializes and maintains network communication parameter values. It provides mechanisms for joining and leaving the network as well as managing dedicated and shared network resources. Additionally, the network manager is responsible for collecting and maintaining diagnostics about the overall health of the network and reporting to host-based applications.
A feature that is desirable in industrial sensor networks is the ability to track people and assets on the plant floor and subsequently the capability of detecting intruders. Previous methods for implementing location detection required the installation of various sensors, beacons, and detectors along with a separate infrastructure to carry out the location detection and reporting. These systems are often too expensive to implement separately which results in sensor network systems that do not include location information. A method to use an existing wireless sensor network infrastructure for location detection is needed.